S1W2 L1- Circulatory Physiology- Cardiac excitation-contraction coupling- Ruth Norman

Question 1

what does EC-CC describe

Answer 1

converting electrical stimulus to mechanical response

Question 2

t-tubule

Answer 2

extensions of plasma membrane which invaginate into the centre of cardiac cells (typically around z discs)

Question 3

SR

Answer 3

sarcoplasmic reticulum

Question 4

what is the SR made up of

Answer 4

longitudinal and terminal elements

Question 5

where are the terminal cisternae of SR located

Answer 5

close to t-tubules

Question 6

what are the terminal cisternae

Answer 6

where the SR meets the t tubules to form Ca2+ release site

Question 7

why do atrial myocytes lack t tubules

Answer 7

the are not requires to produce as much force as ventricular myocytes

Question 8

RyR2

Answer 8

ryanodine receptor 2, cardiac myocyte specific ryanodine receptor, cA2+ release channel

Question 9

LTCC

Answer 9

L-type calcium channel, located in wall of t tubule

Question 10

where do RyR2 and LTCC create a junction between and junction name

Answer 10

extraC and intraC calcium stores: Dyad junction

Question 11

how does Dyad facilitate Ca2+ induced Ca2+ release
(cardiac excitation-contraction coupling)

Answer 11

packed full of channels to allow intra and extra coupling

Question 12

what causes LTCCs to open
(cardiac excitation-contraction coupling)

Answer 12

AP travelling across surface membrane and depolarising t tubules

Question 13

what causes RyR2s to open
(cardiac excitation-contraction coupling)

Answer 13

Ca2+ enters intracellular space between t tubules and SR through the LTCCs

Question 14

what does the RyR2 channels opening cause
(cardiac excitation-contraction coupling)

Answer 14

Ca2+ flood out of SR to cytoplasm

Question 15

what do spatio-temporal summation of Ca2+ sparks cause
(cardiac excitation-contraction coupling)

Answer 15

Ca2+ transient activating uniform and forceful contraction of the cell (individual calcium releases create a large coordinated calcium signal)

Question 16

significance of the arrangement of RyR2 channels and what does this cause in the cardiac excitation-contraction coupling

Answer 16

causes a wave of Ca2+ release from SR which spreads along musculature

Question 17

where are Ca2+ release sites located in the myocyte and why

Answer 17

z lines around myofibrils
means max diffusion distance to activate myofilaments in 500nm
allows synchronisation of contraction to be maintained

Question 18

function of titin

Answer 18

associated with myosin
helps elasticity within I band

Question 19

A band

Answer 19

thick filaments, mainly myosin

Question 20

I band

Answer 20

thin filaments, mainly actin

Question 21

tropomyosin

Answer 21

long protein associated with actin filament
lies in the groove made by two strands of actin filament

Question 22

what are the three subunits of a troponin complex

Answer 22

Tn-C, cA2+
Tn-I, actin
Tn-T, tropomyosin

Question 23

in the presence of Ca2+, what does the binding of Ca2+ to Tn-C cause

Answer 23

stronger binding of TnC to TnI
TnI can no longer bind to actin
cascade of binding changes
allows myosin to bind to actin

Question 24

what happens when Ca2+ lowered again

Answer 24

Ca2+ ions dissociate from TnC
TnI will bind once again to actin and myosin binding site will be covered

Question 25

three possible pathways of Ca2+ recycling

Answer 25

pumped back into SR
NA+-Ca2+ exchanger
sarcolemma Ca2+ ATPase